While Loop

Updated Dec 23, 2020 ·

Overview

A while loop runs as long as a condition is true, unlike the for loop, which has a set number of iterations.

Example: Printing numbers from 1 to 10.

• Using a For Loop:

  for (let i = 1; i <= 10; i++) {
    console.log(`Iteration ${i}`);
  }

• Using a While Loop:

  let i = 1;                        // Initialize counter outside of the loop
  
  while (i <= 10) {                 // Condition to check
    console.log(`Iteration ${i}`);
    i++;                            // Increment counter
  }

Output:

Iteration 1
Iteration 2
...
Iteration 10

The while loop does the same as the for loop, but the counter and incrementing are handled separately.

Example: Rolling a Dice Until We Get 6

The code below generates a random decimal number between 0 and 6 every time it runs:

let dice = Math.random() * 6;
console.log(dice);

Sample output:

0.8258020006410827 

Since Math.random() returns a decimal between 0 and 1, multiplying by 6 expands the range. However, this does not ensure whole numbers like a real dice roll. To fix this, we can use Math.trunc() to remove decimals and add 1 to make sure it includes 6:

let dice = Math.trunc(Math.random() * 6) + 1;
console.log(dice);

Now that we know what logic to use, we can now create the loop. We don’t know yet how many times we’ll need to roll, so a while loop is perfect.

let dice;

while (dice !== 6) {
  dice = Math.trunc(Math.random() * 6) + 1;
  console.log(`You rolled a ${dice}`)
}

Output (varies each time):

You rolled a 2
You rolled a 5
You rolled a 4
You rolled a 1
You rolled a 6

When you re-run the code, you'll get a different output:

You rolled a 1
You rolled a 3
You rolled a 4
You rolled a 6  

Key Differences: for vs while

Feature	For Loop	While Loop
Counter Required?	Yes	No (optional)
Use Case	Known iterations	Unknown iterations
Condition Placement	In loop definition	Only condition needed

do while Loop

Each loop is useful in different situations

• while loop checks the condition first before running the code
• do while loop runs the code first, then checks the condition

The do while runs the code at least once, even if the condition is false.

let counter = 10;
do {
    console.log(counter);
    counter--;
} while (counter > 0);

Note:

• Starts with do, executes the block
• Checks the condition after running the block
• Runs at least once even if counter is 0 initially

This is useful when you need to execute something before validation.